Bronzing or coloring of metallic surfaces.



UNITED STATES PATENT OFFICE.

QUIBINO SESTINI AND TITORONDELLI, OF BERG-Alto, ITALY.

BIIiOlil'ZIN(:rv R COLORING OF METALLIC SURFACES.

To all whom it may concern;

Be'it known that we, QUmINo SEs'rIm and Trro RONDELLI, subjects of theKing of Italy, residing at Bergamo, Italy, have inv vented certain newand useful Improvements ,out this specification and in the claims todenote not merely the production of the coloration known as bronzin butthe formation of'a coating of an oxi of copper or of iron which servesas a protection to the surface beneath it to prevent further oxidationor corrosion thereof. Prominent among the objects of the'presentinvention is the provision of a process whereby the desired results canbe obtained more rapidly than hitherto. To this end the surface to beprotected or colored is preliminarily coated with an electrolyticdeposit of iron or copper.

According to the present invention a surface is bronzed or colored bydepositing co per or iron electrolytically thereon and subsequentlyoxidizing the said deposited metal; by oxidizing is meant not merely theproduction of a simple oxid but the production'of any compound obtainedby a process which in the broadest chenncal sense may be described as anoxidizing process.

The bath employed according to this invention is preferably 'a hot densealkaline solution containing an oxid either of copper or of ironcombined with an oxid of the alkaline metal present; and the bronzing orcoloring is conveniently effected by first electrolytically depositingthe iron or copper on the surface to be treated in a bath of the kindjust stated and subsequently coloring the said deposit by reversing thecurrent. The density of the solution varies between about 1.25 and 1.55and the temperature at which it is worked is from about 115 C. u

ward, the term density being used .111 this Specification of LettersPatent.

Patented Sept. a, 1918.

Application filed May 15, 1917. Serial No. 168,763

instance, as in all others herein, to indicate the specific weight ofthe solution as compared with that of water.

The process may be carried out by, making the conductin surface anode,or alternately cathode an anode, but finally anode in an electrolytethatis a hot dense alkaline solution such as has been above referred to andthat contains'an oxid either of copper or .of iron combined with an oxidof the alkaline metal present, the said combined substance being eithera ferrite of the alkali metal, or a similar copper compound thereof- Thetemperature of the bath is conveniently between about 120 C. and 140 C.

and its density between 1.3 and 1.5 due to the alkaline content.

In order to provide a bath for the purposes of the present invention,the bath may be prepared, as part of the present invention, byrepeatedly reversing the current through a hot dense alkaline solutionbetween electrodes that are both ofiron or both of copper; the alkalinesolution may be either a caustic alkali or an alkaline carbonate andhave a density between 1.3 and 1.4 and a temperature between about 120C. and 130 C.

A further step provided by the present invention, to be used as and whendesired, consists in immersing the surface that is bein treated, afterit has been electrolytically co ored in a solution of caustic alkalicontaining between about 10% and 20% of a metallic nitrate, or anaromatic nitrate derivative as nitrophenols or nitronaphthols; thedensity of the solution should be about 1.4 and its temperature about140 C.

All or any of the above described steps may be followed by drying thecolored surface and leaving it long immersed in a bath of oil at atemperature of between about 150 C. and 180 0.; the period of immersionmay be in the-neighborhood of about ten minutes and the oil employed isconveniently olive'oil, or a mixture of linseed or mineral oils.

The following examples serve further to disclose the present invention:

An electrolyte is prepared by passing current and repeatedly reversingit between electrodes of the metal to be used, namely either iron orcopper in a bath of hot concentrated alkali. The density of the bath,

minutes.

for a caustic alkali, is between 1.3 and 1.4; equivalent quantities ofcaustic potash or an alkaline carbonate may equally be used.

The temperature of the bath is raised to a point between about 120 C.and 130 C. If the electrodes are of wrought or castiron, or of steel,the repeated reversals of current through it causes an oxid of iron to,be formed and dissolved in or to be combined with the alkali in thebath; apparently the result is the formation of an alka-' line ferritehaving the formula Fe O .Na O or NaFeO If the electrodes are of copper.it is an oxid of copper which is formed and enters into the electrolyteand forms a solution of a compound whose formula is similar to that ofthe iron compound above referred to but with copper as its metallicelement.

vVhen once the electrolyte has thus been prepared it may be usedindefinitely and does not undergo exhaustion.

Assuming iron electrodes to have been used so that the electrolytecontains an iron oxid and the article to be colored is to-be colored abright black, it is immersed in the bath, the bath is brought to atemperature of about 120 C. to 130 C. and the article is made to act ascathode for about 1 to 2 The article does not need to be preliminarilycleaned but may be immersed whether smooth or rusty direct in the bath.The current density employed is about 5 amperes per square decimeter ofthe surface to be colored.

While thus operating as cathode the article is both cleaned and platedwith electrolytic iron. At the end of this period the current isreversed and the article made to serve as anodefor from six to eightminutes.

The result of this step is to form a bright black coating of oxid uponthe article which may, however, be further strengthened and renderedmore adhesive by subsequently immersing it for a few minutes in asolution of caustic soda having a density ofl/l, heated to about 140 C.and containing from 10% to 20% of sodium nitrate. Instead of sodiumnitrate almost any metallic nitrate or aromatic nitro derivative may beemployed in this solution.

If a dull black is desired the current should be reversed at least twoor three times, taking care, however, to make the final direction suchthat the article acts as anode and that the current is continued for atleast two minutes after the oxidation is complete. The completion of theoxidizing action is indicated by the voltage at the terminals of thebath; during the oxidizing process the voltage is in the neighborhood of0.6 volts but rises to between 1.8 and 2 volts when oxidation iscomplete.

The colored articles, whether bright or dull, are dried and immersed forten minutes oxidizing agents may also be added.

in a bath of olive oil heated to between 150 C. and 180 C. Instead ofolive oil a mixture of linseed oil and mineral oil may be employed.Brushing the colored surface causes it to become brighter and brighter.

. If red or yellow shades of coloration are desired, the concentrationof the bath must be increased to about 1.5 and the temperature to about140 C. Nitrate of soda or other When arrangements have been made to dealwith articles by a regular routine .the complete treatment of each batchtakes from ten to fifteen minutes so that a batch is fully treated inapproximately that time.

If it is desired to use a copper surface and color it the aboveprocesses described with reference to iron may be employed, using,however, copper electrodes and employing the conditions of temperatureand concentration of the electrolyte given above for the blackcoloration of iron. The coloration is understood to be due to theformation of a closely adhering layer of oxid of iron or of copper asthe case may be on the surface of the anode.

In a modified form of the process, the surface to be colored is coveredwith a deposit of electrolytic iron or copper which is subsequentlyoxidized by a simple immersion in an alkaline oxidizing solution, suchas a solution of nitrate of sodium or other metallic nitrate, oraromatic nitro derivative.

' Theprocess, according to this invention, is easy to carry out andeconomical; the consumption of energy does not ordinarily exceed onewatt hour per square decimeter of the surface treated. The consumptionof the electrolyte is so slight as to be negligible.

The-heating of the bath may be carried out in any desired manner, butpreferably by means of gas or electricity.

Havingnow particularly described and ascertainedthe nature of our saidinvention, and in what manner the same is to be performed, we declarethat what we claim is:

1. The herein-described process of electrolytically coloring metallicsurfaces, which consists in temporarily inserting the object to betreated, as a cathode, in a hot, dense alkaline solution containing anoxid of the metal to be deposited combined with an oxid of the alkalimetal present; passing current through the electrolytic bath to depositon the surface of said object a film of the first-mentioned metal; andexposing the surface so treated to oxidizing conditions in an alkalinebath. V

2. The herein-described process of electrolytically coloring metallicsurfaces, which consists in temporarily inserting the object to betreated, as a cathode,-in a hot, dense alkaline solution containing anoxid of the metal to be deposited combined with an oxid of the alkalimetal present; passing current through the electrolytic bath de osit onthe surface of said object a film of t e firstmentioned metal; andtemporarily'reversing the passage of the current through the bath andinserting the said object therein a s an. anode, so as to set up anoxidizing condition in the said bathfor action on the surface sotreated.

mentioned metal and oxidizing the surfaceso treated in an alkaline bathcontaining an oxidizing compound. a

4. The herein-described process of electrolytically coloring metallicsurfaces, which consists in temporarily inserting the object to betreated, as a cathode, in. a hot,

- dense alkaline solution containing an oxid of the metal to bedeposited combined with an 'tures.

oxid of the alkali metal present and an alkaline nitrate; passin currentthrough the electrolytic bath to eposit on the surface of said object afilm of the first-mentioned metal and exposing the surface so treated tooxidizing conditions in an alkaline bath.

' 5. The herein-described process of electrolytically coloring metallicsurfaces, which consists in passing current and repeatedly reversing itbetween electrodes of the metal to be deposited in, a bath of hotconcentrated alkali to form an electrolyte comprising an oxid of thefirst-named metal combined with an oxid of the alkali metal present;temporarily inserting the object to be treated, as a cathode, in saidelectrolytic bath to deposit a film of said first named metal on thesurface of said object; and exposing the surface'so treated to oxidizingconditions in an alkaline bath.---

In testimony whereof we aflix our signaraor. QUIRINO SEST'INT. DR; TITORONDELLI.

